The Iraqi army will have to destroy Mosul in order to save it — and it’s not clear whether it can do the job even then.

It isn’t so much an army as a vast system of patronage providing employment of a sort for 900,000 people. When fewer than 1,000 jihadis — who belong to a militant group called the Islamic State of Iraq and al-Sham (ISIS) — fought their way into Mosul, Iraq’s second-largest city, over the past few days, most of the government’s soldiers just shed their uniforms and fled.

The government troops never felt comfortable in Mosul anyway, for they are mostly Shia Muslims, and the vast majority of Mosul’s 1.8 million residents are Sunni. Or maybe it’s only 1.3 million people now, for up to 500,000 of the city’s residents are reported to be fleeing the triumphant jihadis. Shias, non-Muslim minorities and even Kurdish Sunnis have faced execution in other areas that have fallen under the control of ISIS.

ISIS began as “Al-Qaida in Iraq” during the American occupation, but it’s the Syrian civil war that turned it into a regional threat.

ISIS actually spent more time fighting other rebel forces in Syria than Syrian President Bashar al-Assad’s regime, but it gained recruits from all the Sunni Arab countries just by being on the right side. It also got access to the money and arms that were flowing into Syria for the anti-government forces. In the past two years, it has established effective control over most of sparsely populated eastern Syria, and it started moving back into western Iraq in force late last year.

In January, it seized the city of Fallujah in Anbar province, only 100 kilometres west of Baghdad, and the Iraqi army was unable to retake the city, although it had suffered about 5,000 casualties — including 1,000 killed — by the end of April. But at least it stood and fought in Anbar. In Mosul on Monday, it just ran.

The only real fighting force left in Iraq is the Peshmerga — the Kurdistan regional government's army. It is a tough, well-armed force, but it serves what is a separate state in all but name. It apparently still holds the part of Mosul east of the Tigris River, which has a large Kurdish population, but it may not be willing to take the large number of casualties that would be involved in street fighting to recover the main part of the city.

ISIS has sent the occasional suicide bomber into Kurdistan, but it realizes that its main fight is not with the Kurds. Having taken most of Mosul, its forces are advancing not east into Kurdistan, but south through Tikrit (which fell Wednesday) toward Baghdad. It will not try to take Baghdad itself (most of whose seven million people are Shia), but by the end of this month, it could end up in control of most of western and northern Iraq.

At this point, the old Iraq-Syria border would disappear and the Islamic State of Iraq and al-Sham would become a reality, extending 400 kilometres from Mosul and Fallujah in Iraq to Deir-es-Zor, Raqqa and near Aleppo in Syria. It would be mostly desert and it would control only about five million people and almost no oil, but it would be ruled by an Islamist organization so extreme that it has even been disowned by al-Qaida.

The remaining bits of the new regional map would be the western half of Syria, still largely under the control of the Assad regime; the semi-independent state of Kurdistan; and the densely populated, Shia-majority core of Iraq between Baghdad and Basra, hard up against the border with Shia Iran. None of this is inevitable yet, of course. It’s a war, and wars can take unexpected turns. But it’s certainly a possibility.

It’s also a possibility that the war could get wider, as Iran, Saudi Arabia and Turkey all consider whether they need to intervene militarily to protect their own interests. But that’s unlikely to happen this month. Later is anybody’s guess.

Gwynne Dyer is an independent journalist whose articles are published in 45 countries.